This invention relates to development apparatus in electrostatographic copiers and printers for electrostatically developing toner images in such copiers and printers with developer material consisting of charged carrier and toner particles. More particularly, this invention relates to such a development apparatus that produces high quality image development by significantly improving developer material movement, mixing and charging. It does so by preventing significant dusting in such apparatus, as well as, uneven accumulation and depletion of toner particles therein.
It is well known to use toner particles held at a development apparatus in electrostatographic copiers and printers to develop electrostatically formed latent images on an image-bearing member in such copiers and printers. The toner particles may be held alone or as a component of a two-component development material, the second component being magnetic carrier particles.
Typically, the development apparatus used is elongate, front-to-back, and is used to hold, move and mix the development material. Moving and mixing the developer material as such, triboelectrically and appropriately charges the toner and carrier particles therein. Additionally the development apparatus also brings the developer material into applying relationship with the images in the copier or printer to be developed with the charged toner particles of the developer material. Such development apparatus are disclosed, for example, in commonly assigned U.S. Pat. Nos. 4,633,807, 4,634,286, and 4,707,107.
The quality of images developed with toner particles as above, depends significantly on the effectiveness and reliability of the development apparatus in triboelectrically charging the toner and carrier particles, and in consistently maintaining higher concentration levels of toner particles from one end to the other within the elongate development apparatus. As such, the developer material moving and mixing devices of the development apparatus are therefore very important in any efforts at improvimg the quality and reliability of image development by such apparatus.
It has been found however that development apparatus including conventional developer material moving and mixing devices such as ribbon blenders, occasionally and unpredictably move or pump developer material unevenly within the sump portion of the development apparatus. Such uneven pumping or movement of developer material is often accompanied by excessive dusting within the development apparatus, by inadequate mixing and, hence, by inadequate charging of the toner and carrier particles therein. More importantly, such uneven movement or pumping of developer material results in uneven front-to-back accumulation and depletion of toner particles within the development apparatus. The end result, of course, is occasional poor and unreliable quality development of images.
These shortcomings of such conventional development apparatus have been found to be especially true when the developer material is of the type disclosed in commonly assigned U.S. Pat. No. 4,546,060 issued Oct. 8, 1985 in the names of Miskinis et al. Such developer material as disclosed is comprised of insulative toner particles and of carrier particles exhibiting hard magnetic properties.